Reduction of oxides of metals of the chromium group



Patented Mar. 13, i923.

RICHARD EDGAR PEA'RSON AND EUSTACE NEVI-LLE CRAIG, O LONDON, ENGLAND, ASSIGNORS TO DURELCO LIMITED, OF LONDON, ENGLAND, A BRITISH COMPANY.

REDUCTION OF OXIDES F METALS QF THE CHROMIUM GROUP.

Application 1ed July 12, 1921. Serial No. 484,168.

To all whom t may concern:

Be it known that we, RICHARD EDGAR PEARsoN. and EUsTACn NEVILLE CRAlG, subjects of the Kin of Eno-land, both resid- 5 ing at Hanwell, ondon, ngland, have .in-`

vented certain new and useful Improvements in the Reduction of Oxides of Metals of the Chromium Group, of which the following is a specification. This invention is for improvements in or relating to the reduction of oxides of metals of the chromium-group, more particularly for use in the preparation of pressed and sintered bars and the like of these metals.

In classifying the metallic elements the term chromium-group is commonly used to embrace the metals, chromium, tungsten, molybdenum and uranium which have 'certain properties in common and where this term occurs in the present specification and claims it is to be interpreted in its ordinary sense (i. e. as signifying the aforesaid metals).

Many methods have been suggested for reducing the oxides of chromium-group metals to lmetallic form including reduction by powdered aluminium, by powdered Zinc or by carbon, and in the case of the tungsten and the molybdenum which are used for the manufacture of filaments and hooks for incandescent electric lamps, or for the contacts and other small parts of magnetos, ionic valves, and the like, the commonest method of reduction has involved the repeated or long-continued passage of pure dry hydrogen o ver the'heated oxide. Isolated suggestions have been made for the reduction of tun sten and molybdenum by electrolysis of thelr solutionsl or oftheir fused comto pounds. v l Considering the case of the methods commonly in use for the production of tungsten and molybdenum for the filaments and wiresof incandescent lamps, the hydrogen reduction process referred to above -is open to several objections. The heating operations and the'supply o'f hydrogen are expensive. The metallic powder-produced by the reduction may very easily be brought into a condition in which it cannot be pressed into bars or sintered. Further for the said process it is essential to use-the pure oxide (such as W03) free from soda, iron and the like, and it is a difficult and sometimes expensive matter to puriv the metallic oxide from such materials w ich may be injurious or disadvantageous in the subsequent treatment or use ofthe tungsten or molybdenum. One objectof this invention is to facilitate the removal of impuritieaand the production of the metal in form well suited for the preparation of pressed and sintered bars or the like.

This invention comprises a process for the reduction to lower oxide of the tri-oxide of a chromium-group metal which process consists in immersing al cathode in an intimate mixture (such as a paste) of the powdered oxide and an electrolyte in which it 1s. insoluble (such as an aqueous solution of sulphuric acid) and effecting reduction to lower oxide by passing a direct current through the mixture.

It is to be understood that the term trioxide includes both the anhydrous and thel hydrated forms of this oxide.

Preferably the paste of powdered oxide and electrolyte is contained in a porous pot or other cathode chamber surrounding the cathode.

The invention also com rises a process for the production of metalic powder for use in the manufacture therefrom of pressed and sintered bars and the like, consisting in reducing the tri-oxide of a chromiumgroup metal as hereinabove described, washing the reduced product until substantiall free from impurities, and hea-ting the pro uct in hydrogen in the known manner to cmplete the reduction.

The intimate' mixture or paste may be agitated during reduction and in the case of molybdenum this is particularly advanta cous.

onvenientl the cathode comprises a number of acidresisting metallic rods (say of nickel-chromium alloy). Any suitable metal may be used as cathode, but if the metal selected be soluble in the electrolyte as zinc is in sulphuric acid, the cathode and electrolyte must not be allowed to remain in contact without current passing.

The invention also comprises a method of carrying outv the foregoing process in which the anode is surrounded with a material which it is desired tol oxidize and which oxidizes in preference to the anode. For example, with a lead anode, waste `molybdenum lmay be packed around the anode,

whereby the oxygen produced by the elec'-v trolysis converts the molybdenum into pow-'f1' dered oxide of molybdenum, which can be used for the production of fresh molybde- 'l'o numppowder. Lead and carbon are suitable materials for use as an anode. rlhe following is a description, by way-of example, ofpne preferredmethod of carry- L ing out this invention as appliedto the treatment of trioxide of tungsten, the ligure of the drawings being illustratiuefof a suitable form of apparatus. a rlhe `apparatus comprises any desired. number vof electrolyt'ic cells, e. g. large rectangular jars 1. of glass or earthenware. The electrolyte is a solution ofsulphuric acid of specific gravity 1.2. ln each jar is a porous pot 2 for the anode and a porous pot 3 for the cathode.

rod 4 ofwlead. rlhe cathode` consists of a number (say about of thin rods 5 oi nickel-chromium alloy connected at their l upper ends to a. metal contact plate 6 and extending down into the cathode pot. The

v 30 agitator consists cfa horizontal metal ring 7 embracing the outside of the cathode rods,

and connected by radialspoke's 8 to a central vertical rod which can slide through the top plate 6 of the cathode. rllhis agitator preferably forms part of the cathode. A

' rlhe powdered oxide of tungstenfWO3 is mixed into a paste (like paint) with the z dilute -sulphuric acid and introduced into the cathode porous pot. (F or example,V 900 grm. of AWO*8 may be used with 150 cc. of dilute sulphuric acid, sp. gr. for each pot.)

1 The electrodes are connected to any suit-v able sourceof direct current at a voltage of say 6 .volts, which may rise slightly say to 7 volts during the process,and reduction is continued to the 'A desired extent, the paste.

f' being stirred from time to time. The avera e working temperature of the/reaction is "*'b'etween 40? C. and 60 C., depending upon the current used, a-suitable current being in the nature of 30 amperes, givinga current .density of 0.10 amperes' per square centi- .metre at the cathode and 0.28 amperes per square centimetrelat the anode. J

It is found economical fnot tovcontinue the reduction till the lowest stage of. oxidation 'r is reached but only as far as the production of a lower oxide such as W02, which will not readily re-oxidize 'whenremoved from the apparatus. washed to recover the acid filter. if

The anode consists vof a stout The reduced materia; is.I and to remqive lmpumtfle-s and' #than dried. @Il a vacuun'l land can readilybe'further reduced by heating in a current'of hydrogen to a metallic lpowder which is peculiarly well adapted to be ressed into rods or bars and sintered.

o t is'foundrthat'the presence in the paste 75' or the electrolyte of certain soluble metallic' f salts of which the metal is more easily oxidizable than the tungsten may be advantageps in hastening or facilitatin the reaction. or example, zinc .sulphate 'as been suc- 80 ces'sfully employed. A 4

- In the anode compartment the lead anode would normally be oxidized by the oxygen evolved by the electrolysis. The anode pot may therefore be filled with a material which 8E it is desired to oxidize and Which oxidizes in preference to the lead anode. For example, scrap or waste molybdenum, such as scrap wire and the like, may 'be pakedr around the anode, and inthe course of theelectrolysis this molybdenum is converted I into powdered oxide of molybdenum which can `be used for the production vof fresh molybdenum powder. l

In any case,however,V any oxidized -lead compounds produced-in the anode compartment may be readily reconverted int-o metal lic lead.` l

This process dispenses vwith the 1diilicult and elaborate steps at present necessary for removing rsoda, iron etc. from W03. It Aalso effects a substantial saving in hydrogen land fuel, which are normally used in t-he present reduction processes. An important result of the process according vto this invention is the finely divided state ofthe product.

lt will be understood that the nature o the electrodes and of the electrolytel may be varied; various means may be employed'for a cathode in anintimate pasty mixture 7of 120` the powdered oxide and an electrolyte in.

.which it is insoluble, and vpassing'fa direct current through the mixture. l

, A. process .for the reduction to lower v Ao'xlde. of the tri-oxide of' tungsten, which 125 Aoo ns'istsin.,immve'rsing a cathode in an intimate .pasty`mixturel of the powdered oxide` fand; anelectrolyte' in which it is insoluble;4

passing"` a@ direct current throughthe 'I A l l d@ "a cathode comprising a number of acid-resisting metallic rods in an intimate pasty` 3. A process for the reduction to lower oxide of the tri-oxide of a chromiumgroup metal which consists in immersing a cathode in an intimate pasty mixtureof the powdered oxidevand an aqueous solution of sulphuric acid and passing a direct current through the mixture.

4. A' process for the reduction tolower oxide of the tri-oxide of a chromiumgroup metal which consists inimmersing mixture of the powdered oxide and an acid electrolyte in which the oxide is insoluble,l

and passing a direct current through the mixture. 5. A process for the reduction to lower oxide of the tri-oxide of a chromiumgroup metal which consists in immersing a cathode comprising a number of rods of nickel-chromium alloy in an intimate pastyl mixture of the powdered oxide and an'aqueous solution of sulphuric acid, and passing a direct current'through the mixture.

6. VA process for the reduction to lower oxide, of the tri-oxide of a chromiumgroup metal which 'consistsin obtaining within a porous cathode chamber an 'intimate pasty mixture ofthe powdered oxide and an electrolyte in which it is insoluble, immersing a cathodel in said mixture, and passing a direct `current therethrough.

7. A process for the reduction to lower oxide, of the tri-oxide of a chromiumgroup metal which consists in immersing a cathode in an intimate pasty` mixture of thel powdered oxide and an electrolyte in which it is insoluble, adding to said mixture a soluble metallic salt, the metal of which is more easily oxidizable than that of theoxide to be reduced, and passing a direct current through the mixture.

8. A process for the reduction to lower oxide, of the tri-oxide of a chromiumgroup metal at the cathode of an electrolytic cell and the simultaneous oxidation of material at the anode, which process consists in immersing the cathode in an intimate mixture of the powdered oxide to be re duced and an electrolyte in which said oxide is insoluble, surrounding the anodeA withl material which it is desired to oxidize and which oxidize's ,in-preference to the anode, and -passing a direct current through the cell.

9. A process for the reduction toy lower oxide, of the tri-oxide of-a chromiumgroup metal at the cathodeof an electrolytic cell and the simultaneous oxidation of material at the anode, which process Consists in-introducin into a porous pot surrounding the'cathoe an intimate pasty mixture of the powdered oxide to be reduced and an electrolyte in which it is insoluble-intro` w y ducing into a porous pot surrounding'the f ltvr process for the' reduction'- tov lower anode material which it is desired to oxidize and which oxidizes in preference to the anode, and passing a direct current through the cell.

10. A process for the reduction to lower oxide of the ltri-oxide ofv a chromiumgroup metal at the cathode of an electrolyticcelhand the simultaneous oxidation of molybdenum at the anode, which process consists in immersing the cathode in an intimate mixture of the powdered oxide andl an electrolyte in which it is insoluble, surrounding a lead anode with waste molybdenum, and Ipass-ing a direct current through the cell.

11. For the production from the tri-oxide of a chromium-group metall of metallic powder for use in the manufacture therefrom of pressed and sintered bars, a process consisting in immersing a cathode in an intimate pasty mixture of the powdered trioxide and an electrolyte in which it is insoluble, p-assing a direct current through the mixture, was-hing the reduced product until substantially free from impurities and heating the product in hydrogen in thel known manner to complete the reduction. i

12. A-process for the production of tungsten powder for use in the manufacture vr.therefrom of pressed and sintered bars, which process consists in immersing a cath-- ode in an intimate pasty mixture of the powdered tri-oxide of tungsten and an electrolyte in which it isnso'luble, passing a direct current through the mixture, washing the reduced product until substantiall free from impurities, and heating the pro uct in hydrogen in the known manner to complete the reduction.

13. A process for the reduction to lower we oxide of 'the tri-oxide of tungsten, which consists in immersing a cathode comprising a number of acid-resisting metallic rods in an intimate pasty mixture (of the powdered oxide and an acid electrolyte in which the ilo,

oxide is insoluble and passing a direct current through the mixture. 14. A process for the reduction to lower oxide of the tri-oxide of tungsten, which consists in immersing a cathode comprising M5 a number of rods of nickel chromium-alloy in an intimate pasty mixture ofpowdered oxide and an aqueous solution of sulphuric acid, andpassing a direct current through `the mixture. 120 15. -A process for the reduction to lower oxide of tri-oxide. of tungsten, which consists in immersing a cathode in an intimate pasty mixture of the powdered oxideand an electrolyte in which it isinsoluble, adding to said mixture 'a soluble metallic salt, the metal of which is more' easil oxidizable through the mixture.

oxidel of the tri-oxide of tungsten et the cathode'of an electrol ic cell amd the simulmucous' oxidation o molybdenum et the anode, which process conslsts 11n lmmerrsmg the cathode in am. intimate mixture of the 'f 'powdered oxide mld am electrolyte in which it is insoluble, surroundng e lead anode .with waste molybdenmvm-jm'ld pessig ai diji-v MGHARD EDGAR PEARsoN EUSTACE Novum clame.A 

